A conventional image-forming apparatus, such as a printer and a facsimile machine, includes a sheet accommodating portion configured to accommodate a stack of sheets therein (such as a sheet tray and a sheet cassette), and a sheet-feed roller configured to feed each of the sheets stacked on the sheet accommodating portion. The sheet-feed roller is made from material having high friction coefficient such as rubber. Each sheet is fed by friction force generated between the sheet-feed roller and the sheet upon rotation of the sheet-feed roller.
Various kinds of sheets are used in the image-forming apparatus depending on intended purposes of use. Among various kinds of sheets, glossy paper (calendered paper) is known as sheets having high rigidity and high surface friction coefficient. In case of a stack of such sheets having high friction coefficient at each surface, a large frictional force is generated between the stacked sheets, generating large sheet-feeding resistance when the sheet-feed roller feeds the sheets. If the frictional force between the sheets becomes larger than the frictional force between the sheet and the sheet-feed roller, rotation of the sheet-feed roller may stop on the sheet so that a sheet-feeding operation can no longer be performed.
Conceivably, in order to avoid a sheet-feeding failure, frictional force between the sheet-feed roller and the sheet may be increased. The frictional force generated between the sheet-feed roller and the sheet may vary depending on a material of the sheet-feed roller, and an area of contact between the roller and the sheet. That is, the frictional force between the sheet-feed roller and the sheet can be increased by providing a sheet-feed roller made from a material having high friction coefficient, or by increasing the area of contact between the roller and the sheet.
Japanese Patent Application Publication No. 2010-037047 discloses a sheet-feeding device using a belt for feeding sheets, rather than a sheet-feed roller. Since the belt can make contact with each sheet with a larger area than the sheet-feed roller does with each sheet, the sheet can be fed with an increased frictional force generated by the belt, restraining occurrence of non-feeding of the sheet.